DatagramSocket將隨機停止接收數據包（有時仍會收到）

Question

我試圖在Java中實現TFTP客戶端。客戶端在本地主機上工作良好，有時會通過網絡發送到TFTP服務器。但是，有時我的DatagramSocket會隨機停止接收數據包。它會發送一個讀/寫請求，但它永遠不會收到服務器嘗試發回的下一條消息。我已經檢查過Wireshark，並且服務器確實收到並嘗試發送。在需要的地方關閉防火牆。無法弄清楚問題所在。這裏是我使用的代碼：

public class TFTPClient { 
String filename; 
String mode; 
boolean read; 
PacketBuilder builder; 
String IP; 
JFrame frame; 
public TFTPClient(String uifilename, String uimode, boolean uiread, String uiIP, JFrame uiFrame){ 
    this.filename = uifilename; 
    this.read = uiread;  
    this.mode = uimode; 
    this.IP = uiIP; 
    builder = new PacketBuilder(); 
    this.frame = uiFrame; 
} 


/* 
* Method choses between reading a file and writing a file based on boolean selected in main UI. 
*/ 
public void startTFTP() throws IOException{ 
    if (read){ 
     readFile(); 
    } 
    else{ 
     writeFile(); 
    } 
} 
/* 
* Method is used for writing a file 
*/ 
private void writeFile() throws IOException{ 
    byte[] WRQ = builder.getWRQ(filename,mode); 
    String filenameAndExtension = filename; 
    RandomAccessFile f = new RandomAccessFile(filenameAndExtension, "r"); 
    byte[] fileBytes = new byte[(int)f.length()]; 
    f.read(fileBytes); 
    f.close(); 



    DatagramSocket TFTPSocket = new DatagramSocket(); 
    TFTPSocket.setSoTimeout(5000); 


    //create the packet and send to port 69 of the given IP 
    DatagramPacket wrqPacket = new DatagramPacket(WRQ, WRQ.length, 
      InetAddress.getByName(IP), 69); 

     try { 
      TFTPSocket.send(wrqPacket); 
     } catch (IOException e) { 
      e.printStackTrace(); 
      System.exit(1); 
     } 
     byte[] ackByte = new byte[4]; 
     DatagramPacket ackPacket = new DatagramPacket(ackByte, 
       ackByte.length); 
     int blockNumber = 0; 
     DatagramPacket dataPacket; 
     boolean terminateOnNextAck = false; 
     boolean needExtraDataPacket = false; 
     int currentIndex = 0; 
     while(true) 
     { 
      TFTPSocket.receive(ackPacket); 
      System.out.println("Server acked " + ackByte[3]); 
      System.out.println("Expected ack " + blockNumber); 

      blockNumber++; 

      if(terminateOnNextAck){ 
       break; 
      } 


      byte[]DATAdata; 
      if (needExtraDataPacket){ 
       DATAdata = new byte[0]; 
       terminateOnNextAck = true; 
      } 
      else if (currentIndex + 512 > fileBytes.length){ 
       //This is our last byte. Length will be smaller than 508 
       DATAdata = new byte [fileBytes.length - currentIndex]; 
       terminateOnNextAck = true; 
      } 
      else{ 
       DATAdata = new byte[512]; 
      } 
      if (currentIndex + 512 ==fileBytes.length){ 
       needExtraDataPacket = true; 
      } 
      for (int i = 0; i<DATAdata.length; i++){ 
       DATAdata[i] = fileBytes[currentIndex]; 
       currentIndex++; 

      } 

      byte[] DATA = builder.getData(DATAdata, blockNumber); 


      dataPacket = new DatagramPacket(DATA, DATA.length, 
        InetAddress.getByName(IP),ackPacket.getPort());   
       try { 
        TFTPSocket.send(dataPacket); 
       } catch (IOException e) { 
        e.printStackTrace(); 
        System.exit(1); 
       } 
     } 
     TFTPSocket.close(); 
     System.out.println("Write sucessful"); 

} 
/* 
* Method is used for reading a file 
*/ 
private void readFile() throws IOException{ 
    //Get RRQ packet 
    byte[] RRQ = builder.getRRQ(filename,mode); 
    StringBuffer fileText = new StringBuffer(); 

    DatagramSocket TFTPSocket = new DatagramSocket(); 
    TFTPSocket.setSoTimeout(5000); 
    //create the packet and send to port 69 of the given IP 
    DatagramPacket rrqPacket = new DatagramPacket(RRQ, RRQ.length, 
      InetAddress.getByName(IP), 69); 

     try { 
      TFTPSocket.send(rrqPacket); 
     } catch (IOException e) { 
      e.printStackTrace(); 
      System.exit(1); 
     } 
     byte[] dataByte = new byte[516]; 
     for (int i = 516;i<516;i++){ 
      dataByte[i] = 0; 
     } 
     DatagramPacket dataPacket = new DatagramPacket(dataByte, 
       dataByte.length); 
     System.out.println("Client: Waiting for packet."); 
     DatagramPacket ackPacket; 
     boolean error = false; 
     while(true) 
     { 
      TFTPSocket.receive(dataPacket); 
      System.out.println(TFTPSocket.getLocalPort()); 
      if (dataByte[1] == 5){ 
       error = true; 
       break; 
      } 
      fileText.append(new String(dataPacket.getData(),0,dataPacket.getLength())); 
      byte blockNumbers[] = new byte[2]; 
      blockNumbers[0] = dataByte[2]; 
      blockNumbers[1] = dataByte[3]; 
      byte[] ACK = builder.getACK(blockNumbers); 
      ackPacket = new DatagramPacket(ACK, ACK.length, 
        InetAddress.getByName(IP),dataPacket.getPort()); 

       try { 
        TFTPSocket.send(ackPacket); 
       } catch (IOException e) { 
        e.printStackTrace(); 
        System.exit(1); 
       } 

      if (dataByte[515] == 0){ 
       break; 
      } 
      dataByte[515] = 0; 
     } 

     if (!error){ 
      JOptionPane.showMessageDialog(frame, "Read Successful!"); 
     System.out.println(fileText); 
     } 
     else{ 
      JOptionPane.showMessageDialog(frame,"Error from server: " + new String(dataPacket.getData(),0,dataPacket.getLength())); 
     }  
} 
} 

Answer 1

該問題原來是與Mac OS X的東西。該程序在Windows上運行良好。雖然不完全確定爲什麼。